1. Field of the Invention
The present invention relates to a vehicle door frame made of a material such as an aluminum alloy (light alloy) and a method of producing the vehicle door frame.
2. Description of Related Art
In general, vehicle door frames are made by butt-welding (corner welding) ends (butted ends) of at least a pillar member (e.g., a vertical pillar sash member or a door frame member) and an upper sash member (door frame member). TIG welding or MIG welding is generally utilized to carry out such a welding process. An aluminum alloy extruded product tends to be mainly used as a material for the vehicle door frame instead of a conventional roll-formed product made of an iron-based material for the purpose of weight reduction. An example of such a method of producing a vehicle door frame is disclosed in Japanese Unexamined Patent Publication 2003-412525.
When aluminum-alloy door frame members are joined by welding, it is difficult to check the weld strength. More specifically, TIG welding or MIG welding is a process that joins base materials (base metals) together by melting these base materials while also melting a welding wire or a filler wire; however, it is visually impossible to check the degree (depth) of welding of the base materials merely by looking the surface of the welded portion.